421 research outputs found
Prevention of sidewall redeposition of etched byproducts in the dry Au etch process
In this paper we present a new technique of etching thin Au film in a dual frequency inductively coupled plasma (ICP) system on Si substrate to prevent the redeposition of etched Au particles over the sidewall of the masking material known as veils. First, the effect of the lithography step was investigated. Then the effects of etch chemistry and the process parameters on the redeposition of etched Au particles on the sidewall of the masking material were investigated. The redeposition effect was examined by depositing a thin Ti film over the masking material acting as a hard mask. The results showed that depositing a thin Ti film over the masking material prevents the formation of veils after etching Au in plasma environments for submicron size structures. Based on the results of this study, we propose a new technique that completely eliminates formation of veils after etching Au in plasma environments for submicron size structures
Gravity wave turbulence in a laboratory flume
We present an experimental study of the statistics of surface gravity wave turbulence in a flume of a horizontal size 12×6 m. For a wide range of amplitudes the wave energy spectrum was found to scale as Eω∼ω-ν in a frequency range of up to one decade. However, ν appears to be nonuniversal: it depends on the wave intensity and ranges from about 6 to 4. We discuss our results in the context of existing theories and argue that at low wave amplitudes the wave statistics is affected by the flume finite size, and at high amplitudes the wave breaking effect dominates
School Admissions Reform in Chicago and England: Comparing Mechanisms by Their Vulnerability to Manipulation
In Fall 2009, officials from Chicago Public Schools changed their assignment mechanism for coveted spots at selective college preparatory high schools midstream. After asking about 14,000 applicants to submit their preferences for schools under one mechanism, the district asked them re-submit their preferences under a new mechanism. Officials were concerned that "high-scoring kids were being rejected simply because of the order in which they listed their college prep preferences" under the abandoned mechanism. What is somewhat puzzling is that the new mechanism is also manipulable. This paper introduces a method to compare mechanisms based on their vulnerability to manipulation. Under our notion, the old mechanism is more manipulable than the new Chicago mechanism. Indeed, the old Chicago mechanism is at least as manipulable as any other plausible mechanism. A number of similar transitions between mechanisms took place in England after the widely popular Boston mechanism was ruled illegal in 2007. Our approach provides support for these and other recent policy changes involving matching mechanisms.
A CMOS visible image sensor array using current mirroring integration readout circuitry
This paper reports the development of a CMOS visible sensor array using a high performance readout circuit called Current Mirroring Integration (CMI). The sensor element is a photodiode implemented using n-well and p+ -active layers available in any CMOS process. The current generated by optical excitation is mirrored and integrated in an off-pixel capacitor using the CMI readout circuit, which provides high injection efficiency, low input impedance, almost-zero and stable detector bias, and a high dynamic range. A 16x16 test array is fabricated using a 0.8µm CMOS process. Each detector pixel in the array occupies a 50µm x 50µm area with a fill factor of 60%. Operation of the fabricated test array is verified, and the output dynamic range is measured as 0.5V to 4.8
Fair Allocation of Vaccines, Ventilators and Antiviral Treatments: Leaving No Ethical Value Behind in Health Care Rationing
COVID-19 has revealed limitations of existing mechanisms for rationing
medical resources under emergency scenarios. Many argue that these mechanisms
abandon various ethical values such as equity by discriminating against
disadvantaged communities. Illustrating that these limitations are aggravated
by a restrictive choice of mechanism, we formulate pandemic rationing of
medical resources as a new application of market design and propose a reserve
system as a resolution. We develop a general theory of reserve design,
introduce new concepts such as cutoff equilibria and smart reserves, extend
analysis of previously-known ones such as sequential reserve matching, relate
these concepts to current debates, and present preliminary policy impact.Comment: Keywords: ethical rationing, reserve system, COVID-19, vaccines,
ventilator
Refraction of a Gaussian Seaway
Refraction of a Longuet-Higgins Gaussian sea by random ocean currents creates
persistent local variations in average energy and wave action. These variations
take the form of lumps or streaks, and they explicitly survive dispersion over
wavelength and incoming wave propagation direction. Thus, the uniform sampling
assumed in the venerable Longuet-Higgins theory does not apply following
refraction by random currents. Proper handling of the non-uniform sampling
results in greatly increased probability of freak wave formation. The present
theory represents a synthesis of Longuet-Higgins Gaussian seas and the
refraction model of White and Fornberg, which considered the effect of currents
on a plane wave incident seaway. Using the linearized equations for deep ocean
waves, we obtain quantitative predictions for the increased probability of
freak wave formation when the refractive effects are taken into account. The
crest height or wave height distribution depends primarily on the ``freak
index", gamma, which measures the strength of refraction relative to the
angular spread of the incoming sea. Dramatic effects are obtained in the tail
of this distribution even for the modest values of the freak index that are
expected to occur commonly in nature. Extensive comparisons are made between
the analytical description and numerical simulations.Comment: 18 pages, 10 figure
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